摘要:

AbstractThe crack propagation behaviour of secondary hardened alloy steels having various Ni contents and a 18%Ni maraging steel was studied using modified compact tension specimens under 98–784 kPa hydrogen gas pressure pH2. The effect of Ni content and retained austenite was examined by comparing oil quenched specimens with those cooled to liquid nitrogen temperature. It was estimated from the effect of pH2on the crack propagation rate da/dt that the permeation of hydrogen from the crack tip surface decreased with increasing Ni content in the order 6 or 9, 13, then 18%Ni. It was also estimated that the hydrogen induced embrittlement of grain boundaries decreased with increasing Ni content in the order 6, 9, then 13%Ni and that the embrittlement was greater for the steel containing 18%Ni than for the steel containing 13%Ni. The effect of retained austenite was expected to suppress not the permeation of hydrogen, but the embrittlement of grain boundaries.MST/757

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.6.584

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractOne possibility for surface treatment using lasers is to cause significant changes in surface composition and microstructure. However, techniques for changing composition remain poorly developed and the mechanisms controlling final microstructure are still not fully understood. A very simple technique for supplying alloying additions has been used in the present work to modify a ferritic stainless steel and has been shown to be capable of causing large changes in composition. As-alloyed layers remain fairly inhomogeneous and a second melting is necessary, at which time treatment conditions can be selected to obtain the required microstructural state. There is a relationship between the formation of the microcrystalline layers observed and the cooling rate and the formation of the microcrystalline layers can be analysed in terms of continuous crystal nucleation. As expected, the abrasive wear resistance of the surface layers improved as a result of the increase in hardness.MST/909

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.6.590

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe present investigation was carried out to define a numerical simulation for the semicontinuous copper casting process of circular section ingots. The physical aspect of the process consists essentially of the heat transfer between the forming ingot and the mould apparatus, during which there occurs a transformation in metal phase. The mathematical model consists of a second order partial differential equation solved using the method of finite differences, then the resulting non-linear system of algebraic equations was solved using an iterative method. Using the mathematical model developed in the present investigation, for various mould sizes and casting conditions, it is possible to evaluate temperature distribution in the ingot, the levels of heat flow through the mould wall and during secondary cooling, and the configuration of the liquid/solid interface. The results obtained in the present study were used for an overall verification of the mathematical model.MST/789

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.6.595

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe formability and electrochemical characteristics of aluminium powder coated steel sheets have been determined as functions of the coating sintering time and temperature. The coatings were fabricated on the laboratory scale using a dry powder coating process, followed by rolling to achieve a 10% extension. The sintering temperatures studied were in the range 573–873 K (300–600°C). Coatings were also fabricated using Al–0·16Ti prealloyed powder and their characteristics were studied. Heat treatment temperature in the range 723–748 K (450–475°C) has been found to have a deleterious effect on the coating formability and electrochemical characteristics of both the aluminium and the Al–Ti coatings. This deterioration in properties has been attributed to the change in aluminium powder sintering characteristics in this temperature range. The electrochemical characteristics have also been compared with those of the more commonly used galvanised steel sheets. It has been shown that using this dry powder coating process, aluminium coatings of high formability and corrosion resistance can be fabricated using low economical sintering temperatures of about 623–673 K (350–400°C).MST/552

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.6.605

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA previous treatment of nucleation in gas atomised liquid aluminium alloys has been extended to model more realistically the cooling conditions in a gas atomiser. Previous predictions of the phase which will predominantly nucleate in powder particles, as a function of powder size and composition, are reinforced. Predicted undercoolings are now slightly higher than in the earlier work. Results from this work are compared with recent experiments.MST/1013

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.6.609

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractVickers hardness tests were carried out on specimens of iron in a cold rolled or annealed condition to investigate apparent variation of hardness in the load range 15 g–20 kg. This hardness variation was markedly reduced by lubrication. Therefore, it is suggested that the indentation size effect in these conditions is controlled by friction. Strain hardening seemed to be an important secondary factor.MST/1023

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.6.613

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.6.615

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor